Introduction

Dishes, utensils, kitchen appliances, countertops, and anything else used with non-kosher food, cannot be used for kosher food unless it goes through a process known as “kashering” or “hechsher keilim”. For a few items kashering just involves thoroughly cleaning the item, but for most items kashering also requires submerging the item in boiling water or a similar hot process. The laws of kashering are quite complex, and this article will present the most practical points for the average consumer; readers are encouraged to discuss any questions not covered in this article with their local Orthodox Rabbi. [The article will focus on kashering between non-kosher and kosher, and will not note the minor differences involved in kashering between meat/dairy and pareve, and kashering for Pesach.]

The following items may not be kashered:

China, pottery, earthenware, cement/concrete and enameled pots may not be kashered. The Ashkenazic custom is to not kasherglass, with the exception of glass stovetops discussed below. There is a difference of opinion as to whether plastic and other synthetic materials are included in this rule, and the cRc position is that those materials may be kashered.

Utensils and appliances which cannot be thoroughly cleaned such as those having crevices in which food may accumulate may not be kashered. Some examples of this are sieves, graters, utensils with loose-fitting handles, and bottles with narrow necks.

Materials which might get ruined during the kashering process may not be kashered as the Rabbis were concerned that the person would not kasher properly for fear of ruining the utensil or appliance.

Flatware

Silver, stainless steel, and plastic flatware may be kashered. The process begins with a thorough cleaning, after which the utensil should not be used for 24 hours. A pot of water is brought to a rolling boil, and the pieces of flatware are dropped into the water one at a time. If the water stops boiling at any point, one must wait until it returns to a boil before putting in any more flatware. The custom is to rinse the flatware with cold water after kashering.

Some have the custom to kasher in a dedicated “kashering pot” which is not used for anything else, but most kasher in any pot which is clean and has not been used for 24 hours.

Pots and Pans

Standard metal pots are kashered in the same manner as flatware; consult with your Rabbi if the pot which requires kashering is too large to fit into any other pot of boiling water. Enameled pots and glass pots (e.g. Pyrex) cannot be kashered.

In general, baking, roasting and frying pans cannot be kashered unless they are always used with generous amounts of oil or other grease when cooking. If that is the case, they can be kashered via libun kal which involves cleaning the pans well, not using them for 24 hours and then putting them on an open flame until both the inside and outside of the pan are hot enough to singe paper.

A cRc video with simple instructions on how to properly kasher pots and pans can be found on our website by clicking HERE.

Drinking Glasses

The Ashkenazic custom is that drinking glasses made of glass cannot be kashered if they were ever used for hot beverages or washed with hot water, such as in a dishwasher. If they were never used or washed hot, contact your Rabbi for directions as to how they may be kashered. Drinking glasses made of plastic can be kashered in the same manner as flatware outlined above, and drinking glasses (or anything else) made of ceramic or chinacannot be kashered.

Electric Mixers, Food Processors and Blenders

The motor area of small electric appliances (e.g. mixers, food processor, blenders) is often exposed to foodand is very difficult to clean; it is therefore recommended that they not be kashered (and used) if they were used for non-kosher. Food processors and blenders whose motor area is truly sealed (i.e. they cannot be unscrewed or opened by consumers) are not affected by this issue and may be used after separate bowls and blades are purchased.

Sinks

Stainless steel or Corian sinks may be kashered by cleaning them thoroughly, leaving them unused for 24 hours, and then carefully pouring boiling water from a kettle over all surfaces of the sink and faucet. The strainer covering the sink’s drain should be replaced. Porcelain sinkscannot be kashered. Kosher dishes and other utensils may not be placed in a sink which was not kashered; rather, an insert or basin must be placed in the sink, and all dishes should be put into that insert.

Stovetops and Ovens

Stovetops (ranges) and ovens may be kashered, and the process for doing so is as follows:Stovetops
The most common type of stovetop is a metal grate over an open flame, which is situated on a porcelain surface. Others have electric coils in the place of an open flame or have a glass surface covering electric coils, and the most popular brands for this type of stovetop are Corning and Ceran.
The kashering of all of these stovetops is similar. All parts of the stovetop should be thoroughly cleaned, including scraping residual food from the surface and catch-tray, and not used for 24 hours. Then the fire or coil should be turned to its maximum temperature for one hour. Finally, the knobs, catch trays and all areas between the burners should be treated as non-kashered and kosher food and utensils should not be placed on those areas. [If kosher items were placed on that area, consult with your Rabbi as to their status.] Non self-cleaning oven
The interior and exterior surfaces of the oven must be thoroughly cleaned, the oven should not be used for a full 24 hours, and then turn it should be turned on to its highest temperature for one hour. Self-cleaning oven
A complete self-clean cycle should be run with the racks inside the oven, and then the oven may be used without covering the racks. This kashering may be done even if the oven was not left unused for 24 hours. If the racks are not inside the oven while the self-clean cycle is run, the racks should be kashered separately.Microwave oven
The microwave’s glass platecannot be kashered (or used) and should be removed before kashering begins. To kasher the appliance itself, the microwave must be thoroughly cleaned and not used for 24 hours. Then, a cup of water should be boiled in the chamber for an extended amount of time, until the chamber fills with steam and the water overflows from the cup. If a microwave has a metal grate, it should be kashered in a pot of hot water as described in the Flatware section above.
For convection microwave ovens, the same kashering process as a conventional oven should be followed, paying particular attention to cleaning out the chamber and fan assembly.

A summary of the information about stovetops is included in the following chart.

COMMON BRANDS

KASHERABLE?

COMMENTS

STOVETOPS

METAL GRATES

YES

METAL FLAT TOP

YES

ELECTRIC BURNERS

YES

GLASS TOPS

YES

According to the cRc policy, it can be kashered

OVEN TOPS BETWEEN BURNERS (on gas and electric)

NO

These should be covered

OVEN TOPS BETWEEN BURNERS (on glass tops)

SEE COMMENTS

The area should be covered, if possible. Otherwise, it must be cleaned.

Refrigerators and Freezers

Countertops

The procedure for kashering a countertop is to clean it thoroughly, not use it for 24 hours, and then carefully pour boiling water on all surfaces. Once the countertop is kashered, it may be used without being covered. As noted at the beginning of this article, one may not kasher utensils made of certain materials (ceramic, cement, glass), materials which are not robust enough to withstanding kashering, and any utensil that has cracks, nicks or scratches where pieces of food might get stuck. These same restrictions apply to countertops.

In any situation where the countertop cannot or will not be kashered, it may only be used after being covered with a non-porous material which will not easily rip or tear.

There are many countertop materials available for home use today, with the old favorite being plastic laminate, manufactured by laminating a hard plastic material onto a thin piece of wood. Some popular brands of laminate are Formica, Pionite, Wilsonart, andNevamar. In some cases, there are seams where two pieces of laminate meet, creating the potential for food collecting in that area, and special attention should be paid to cleaning those seams.

Butcher block or wood surfaces are once again becoming popular. Wood may be kashered only if it contains no cracks that might trap food. Some of the popular wood brands on the market are John Boos, Craftart, Spekva, and Omega.

Many kitchens use natural stone such as granite, marble, limestone, soapstone, slate, and onyx for countertops. All of these may be kashered regardless of which sealant is used to coat the stone.

Another material used for countertops is quartz resin, a man-made material made to look like granite or marble. It is different than natural stone in that it is not porous. Therefore the surface does not need to be sealed. Some common brands are Cambria, Silestone, Zodiaq, and Caesar Stone. These may be kashered.

Similarly, there is another countertop material which is made to look like stone but it is actually an acrylic or polyester and therefore easy to maintain. Some popular brands are Corian, Staron, Swanstone, Gibraltar, Surrell, and Avonite. These materials may be kashered if they do not contain any scratches or stains.

There are also glass, ceramic, cement, and porcelain countertops available, with porous grout between each tile. Buddy Rhodes and Cheng Design are popular brands of cement countertop. These countertops may not be kashered and must be covered.

While not used as often in a home, stainless steel, copper, and zinc countertops are also available, and they may be kashered.

There can always be unique situations that might arise in one’s own home. When in doubt, contact your local Orthodox Rabbi. Special thanks to Rick Glickman of “Dream Kitchens” for his assistance with our countertop research.

A summary of the information about countertops is included in the following chart.